Fast rerouting is a mechanism for protecting a Constrain-based Routing Label Switch Path (CRLSP), which protects the basic CRLSP from being influenced by link failures through providing a local backup path. To protect the CRLSP, first, the primary paths of the CRLSP are enabled to have a fast rerouting property through configuration, and if a router detects a failure in a link to be protected, services can be switched from the link with the failure to a backup path, thereby realizing the protection operation.
As shown in FIG. 1, assume that there is a basic link A-B-C-D-E. Link A-G-C is used to protect node B and node B's related links, link B-G-D is used to protect node C and node C's related links, link C-F-E is for protecting node D and the related links thereof, and link D-F-E is used to protect link D-E. For instance, when node C goes wrong, node B switches the network service flow to link B-G-D so that node C can be protected.
There are two methods for implementing fast rerouting in the prior art: bypass and detour. The bypass method for implementing fast rerouting is generally used at present. According to the bypass method, a pre-setup bypass LSP with the fast rerouting property is used to protect multiple LSPs passing the bypass LSP. When a protected link goes wrong, the service on a primary LSP is switched to the bypass LSP and arrives at the next-hop router through the bypass LSP, thus the purpose of protection can be achieved.
There are three kinds of common failures in the present network, including:
1. an interface of a local router being DOWN;
2. a link or node failure being discovered by signaling; and
3. an interface board of a local router going wrong or being invalid.
The conventional technology mainly deals with the first two kinds of failures. If a router detects that there is a failure in an interface or a peer router, service flow is switched to a Bypass tunnel to avoid flow loss. This process is as follows: adding the information of a bypass path to a Next-hop Label Forward Entry (NHLFE) of an outgoing-interface board of the router; when a packet arrives at the outgoing-interface board, sending the service flow being to the interface board of the bypass path according to the bypass path information in the NHLFE if there is an interface failure, and sending out the service flow through an interface of the bypass path. Taking a distributed router for an instance, if a physical interface is DOWN, the interface board is able to find out a CRLSP failure directly and modify the forward information of the NHLFE, thereby switching to the bypass path; and it is needed to inform the interface board to modify forwarding information of the NHLFE if the CRLSP failure is discovered based on the signaling protocol so as to switch to the bypass path. Therefore, by extending the forward entry information of the NHLFE to realize fast rerouting, the first and the second kinds of network failures can be avoided.
However, in the implementation method in the prior art, since the router can determine that packet need to be forwarded by fast rerouting only if the packet has arrived at the outgoing-interface board, the packet has to be transmitted from an incoming-interface board to an outgoing-interface board, and then be forwarded to the interface board of the bypass path from the outgoing-interface board. That is, the transparent transmission between interface boards is required, thus the transmission efficiency is reduced.
Besides, the implementation method can not resolve the problem of flow loss in the third failure well, the reason is that, the NHLFE saved in the interface board will be lost completely when the interface board goes wrong. In a common processing method, the CRLSP is deleted directly and a new one is reset, which leads to flow loss because of the delete and re-setup of the CRLSP. And if the path meeting the condition can not be found, a new CRLSP can not be established, and may further lead to flow interruption.